The present invention is directed to a device or a method for treating the exhaust gas of an internal combustion engine according to the species defined in the independent claims. A device for exhaust-gas treatment is already known from DE 199 04 068 in which ozone produced by an ozone reactor is introduced into the exhaust system of an internal combustion engine. However, at low temperatures a combustion of diesel soot is not ensured since the oxidation catalyst upstream from the particle filter does not oxidize nitrogen oxides at low temperatures, especially below an exhaust-gas temperature of 250 degrees Celsius. As a result, the ozone delivered by the ozone reactor is reacted away by the nitrogen oxides, so that it is unable to have any effect as an oxidant in the particle filter.